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Impedimetric wearable sensors are a promising strategy for determining the loss of water content (LWC) from leaves because they can afford on-site and nondestructive quantification of cellular water from a single measurement. Because the water content is a key marker of leaf health, monitoring of the LWC can lend key insights into daily practice in precision agriculture, toxicity studies, and the development of agricultural inputs. Ongoing challenges with this monitoring are the on-leaf adhesion, compatibility, scalability, and reproducibility of the electrodes, especially when subjected to long-term measurements. This paper introduces a set of sensing material, technological, and data processing solutions that overwhelm such obstacles. Mass-production-suitable electrodes consisting of stand-alone Ni films obtained by well-established microfabrication methods or ecofriendly pyrolyzed paper enabled reproducible determination of the LWC from soy leaves with optimized sensibilities of 27.0 (Ni) and 17.5 kΩ %

Electrochemical techniques are commonly applied to micro total analysis system (μTAS) devices mainly due to its high sensitivity and miniaturization capacity. Among many electrochemical techniques, capacitively coupled contactless conductivity detection (C4 D) stands out for not requiring direct electrode-solution contact, avoiding several problems such as electrolysis, bubble formation, and metal degradation. Furthermore, the instrumentation required for C4 D measurements is compact, low cost, and easy to use, allowing in situ measurements to be performed even by nonspecialized personal. Contrarily, the production of metallic electrodes and microchannels adequate for C4 D measurements commonly requires specialized facilities and workers, increasing the costs of applying these methods. We propose alternatives to batch manufacture metallic electrodes and polymeric microchannels for C4 D analysis using more straightforward equipment and lower-cost materials. Three devices with different dielectric layer compositions and electrode sizes were tested and compared regarding their analytical performance. The constructed platforms have shown a reduction of more than 64% in cost when compared to traditional techniques and displayed good linearity (R2 ≥ 0.994), reproducibility (RSD ≤ 4.07%, n = 3), and limits of detection (≤0.26 mmol/L) when measuring standard NaCl samples. Therefore, the proposed methods were successfully validated and are available for further C4 D applications such as diagnosis of dry-eye syndrome.

Electrochemical cells for direct conversion of solar energy to electricity (or hydrogen) are one of the most sustainable solutions to meet the increasing worldwide energy demands. In this report, a novel and highly-efficient ternary heterojunction-structured Bi4O7/Bi3.33(VO4)2O2/Bi46V8O89 photoelectrode is presented. It is demonstrated that the combination of an inversion layer, induced by holes (or electrons) at the interface of the semiconducting Bi3.33(VO4)2O2 and Bi46V8O89 components, and the rectifying contact between the Bi4O7 and Bi3.33(VO4)2O2 phases acting afterward as a conventional p–n junction, creates an adjustable virtual p–n–p or n–p–n junction due to self-polarization in the ion-conducting Bi46V8O89 constituent. This design approach led to anodic and cathodic photocurrent densities of + 38.41 mA cm–2 (+ 0.76 VRHE) and– 2.48 mA cm–2 (0 VRHE), respectively. Accordingly, first, this heterojunction can be used either as photoanode or as photocathode with great performance for artificial photosynthesis, noting, second, that the anodic response reveals exceptionally high: more than 300% superior to excellent values previously reported in the literature.

The frequently underestimated effects of “in air” thermal treatment processing conditions such as temperature, duration, and heating and cooling rates in the design and efficiency of photoelectrodes fabricated for academic studies onto the most common commercial transparent conductive glass substrate i.e. fluorine-doped tin oxide (FTO) were investigated by XRD, XPS, SEM, conductive AFM, electrochemical impedance spectroscopy (EIS) as well as direct current (DC) and photoelectrochemical (PEC) measurements. The PEC response of Hematite photoanode thin films consisting of short nanorods thermally treated at 400 °C and 800 °C upon fast or extended time conditions is inhibited by factors such as crystallinity, Sn diffusion, or substrate integrity. A “fast” thermal treatment in air at 750 °C provided the best synergy between charge transfer resistance, Sn-diffusion from the FTO substrate, nanorod dimensions, reduced recombination, improved charge separation and minimized substrate damage. This study does offer valuable fundamental and practical insights for a better understanding of the benefits and drawbacks of photoelectrode thermal processing, which is critical for the improvement of the PEC performance-reproducibility relationship for FTO-based solar water splitting systems and devices.

This work examines the role of oxygen supply in the improvement of the hydrogen peroxide (H

Screen-printed electrodes (SPEs) coupled with flow systems have been reported in recent decades for an ever-growing number of applications in modern electroanalysis, aiming for portable methodologies. The information acquired through this combination can be attractive for future users with basic knowledge, especially due to the increased measurement throughput, reduction in reagent consumption and minimal waste generation. The trends and possibilities of this set rely on the synergistic behavior that maximizes both SPE and flow analyses characteristics, allowing mass production and automation. This overview addresses an in-depth update about the scope of samples, target analytes, and analytical throughput (injections per hour, limits of detection, linear range, etc.) obtained by coupling injection techniques (FIA, SIA, and BIA) with SPE-based electrochemical detection.

Tests of the electroflocculation technique were performed on the effluent from the washing of intermodal terminal machines with iron (Fe) and aluminum (Al) electrodes to determine which electrode would have better efficiency and viability of the effluent treatment rate. For the evaluation, pH, turbidity, conductivity, alkalinity and acidity were determined. In this work a bench electrolytic reactor was used in the experimental electroflocculation unit that consists of an acrylic reactor, with a capacity of 6 liters, measuring 30 cm x 15 cm x 20 cm with a sample collection point on the bottom side. The electrolytic cell has 6 iron or aluminum plates arranged in parallel with dimensions of 14 cm x 14 cm x 0.2 cm connected to an external alternating current power source. The results show an increase in pH and alkalinity, reduction in acidity and electric conductivity for both electrodes, however the iron had the better performance. In addition, in the turbidity analysis a reduction in the value for both electrodes, noticing better results for the iron electrode. In view of the results, it was found that iron has a better performance in efficiency and viability in the treatment of machine washing effluent by electroflocculation than aluminum. Testes da técnica da eletrofloculação foram realizadas no efluente da lavagem de máquinas de terminais intermodais com eletrodos de ferro (Fe) e alumínio (Al) para determinar qual eletrodo teria melhor eficiência e viabilidade de taxa de tratamento do efluente. Para a avaliação foram determinadas pH, turbidez, condutividade, alcalinidade e acidez. Neste trabalho foi utilizado um reator eletrolítico de bancada na unidade experimental de eletrofloculação que consiste em um reator de acrílico, de capacidade de 6 litros, medindo 30cmx15cmx20cm, com ponto de coleta de amostra na lateral inferior. A célula eletrolítica conta com 6 placas de ferro ou de alumínio dispostas em paralelo com dimensões de 14cmx14cmx0,2cm ligadas a uma fonte externa de energia de corrente alternada. Nos resultados foram observados: aumento do pH e da alcalinidade, redução da acidez e da condutividade elétrica para ambos os eletrodos, porém, com melhor desempenho para o ferro. Além disso, na análise de turbidez obteve-se uma redução do valor para ambos os eletrodos, notando-se melhores resultados para o eletrodo de ferro. Frente aos resultados, constatou-se que o ferro tem melhor desempenho na eficiência e viabilidade no tratamento de efluente da lavagem de máquinas por eletrofloculação.

Made available in DSpace on 2021-06-25T11:00:01Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01. Added 1 bitstream(s) on 2021-07-15T15:05:32Z : No. of bitstreams: 1 S0103-50532021000601213.pdf: 2507374 bytes, checksum: e6299daa4be75b8399f2f57031ee3012 (MD5) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) The sol-gel technique has drawn considerable attention in the area of biomolecules immobilization by virtue of its intrinsic properties including chemical inertness, thermal stability, and good biocompatibility. The present work reports the development of a bio-sensing methodology which involves the immobilization of horseradish peroxidase enzyme (HRP) on pencil graphite electrode (PGE) using TiO2 sol-gel and its application for 5-aminosalicylic acid (5-ASA) determination in pharmaceutical formulations. TiO2 sol-gel film was deposited on the PGE surface by dip coating, and the HRP enzyme was immobilized on the film by adsorption and cross-linked binding using glutaraldehyde. The analytical performance of the methodology was investigated through amperometric measurements at -0.08 V in the presence of 5-ASA (electron mediator) and hydrogen peroxide (substrate). The biosensor was successfully applied for 5-ASA determination, where limits of detection and quantification of 3.3 and 10.0 μmol L-1, respectively, were obtained. The application of the methodology for 5-ASA determination in pharmaceutical formulations led to satisfactory recovery rates ranging from 80 to 98%. The biosensor developed in this work is simple, inexpensive and has the potential to be applied for the determination of other pharmaceutical compounds, which also act as electron mediators in the catalytic cycle of HRP. Departamento de Química Analítica Físico-Química e Inorgânica Instituto de Química Universidade Estadual Paulista (Unesp), Rua Professor Francisco Degni 55 Departamento de Química Analítica Físico-Química e Inorgânica Instituto de Química Universidade Estadual Paulista (Unesp), Rua Professor Francisco Degni 55 CNPq: 465571/2014.0

Flexible graphite sheets or graphite paper are conductive substrates produced in large scale for use in a wide range of applications, such as in telecommunications, lighting, computer and peripherals, power conversion, and heat generating semiconductors (low-cost material). In this paper we show, for the first time, that commercially available graphite sheets can be used in the as-received condition for the construction of disposable electrodes with excellent performance for electroanalysis (comparable to glassy carbon). Nine different graphite sheets were evaluated by different techniques, such as scanning electron microscopy (SEM), Raman spectroscopy, cyclic voltammetry, square wave voltammetry, and amperometry. The obtained results revealed the existence of large variations between different commercially available materials (not all the sheets work well as sensors in the as-received condition). Our studies have shown that there are commercial flexible graphite sheets with higher electrical conductivity and superior homogeneous composition, which are ideal for use as disposable unmodified or modified sensors. The quality of the results obtained with graphite sheets are dependent on the type of material selected as substrate. However, repetitive results are obtained if the same material is always used. The graphite sheets were coupled to low cost 3D-printed cells forming easy to use disposable devices. The performance of the disposable devices was evaluated using ferri-ferrocyanide and ferrocene probes, dopamine (LOD = 0.7 μmol L−1), catechol (LOD = 0.8 μmol L−1), ciprofloxacin (LOD = 5.9 μmol L−1), cadmium (LOD = 0.013 μmol L−1), and lead (LOD = 0.07 μmol L−1) as model analytes. According to our knowledge, the electroanalytical performance of graphite sheets demonstrated here surpasses previously reported results.

Made available in DSpace on 2020-12-10T19:56:24Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-04-13 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Impedimetric D-Xylose and D-Arabinose sensors was development from composite electrodes of graphite and histological paraffin, modified with functionalized multi-walled carbon nanotubes (FMWCNTs) based on molecular imprinted poly-o-phenylenediamine (poly-o-PD). The contribution of this work was not only the development of a D-xylose and D-Arabinose MIP impedimetric sensor with good performance, but also the electrodeposition method for FMWCNTs onto surface of graphite composites electrodes with ease of control and reproducibility of the electrodeposition process. The sensors were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), field emission gun scanning electron microscopy (FEG-SEM) and RAMAN spectroscopy. The MIPs sensors for the pentoses have good selectivity, sensitivity in the concentration range of 1.0 x 10(-11) to 1.0 x 10(-10) mol 1(-1) with limit of detection (LOD) of 4.50 x 10(-12) mol 1(-1) for D-Xylose and 4.25 x 10(-12) mol 1(-1) for D-Arabinose. MIPs was applied to determination of pentoses in samples of sugarcane bagasse hydrolysates using the standard addition method and validated by recovery study, which presented satisfactory results between 92.9% and 115.5%. (C) 2020 The Electrochemical Society (ECS). Published on behalf of ECS by IOP Publishing Limited. Sao Paulo State Univ, Engn Energy, UNESP, Campus Rosana, BR-19274000 Rosana, SP, Brazil Univ Sao Paulo, Inst Phys, BR-13560970 Sao Carlos, SP, Brazil Univ Nova Lisboa, Fac Sci & Technol, Phys Dept, CEFITEC, Campus Caparica, P-2829516 Caparica, Portugal Sao Paulo State Univ, Engn Energy, UNESP, Campus Rosana, BR-19274000 Rosana, SP, Brazil FAPESP: 2017/09123-9 FAPESP: 2017/09492-4 CAPES: 88887.375050/201900

Enzyme immobilization on solid conducting surfaces faces challenges for practical applications in technologies such as biosensors and biofuel cells. Short-term stability, poor electrochemical performance, and enzyme inhibition are some unsolved issues. Here, we show a simple methodology for bilirubin oxidase (BOD) immobilization on carbon-based gas diffusion electrode for four-electron electrochemical oxygen reduction reaction. BOD is incorporated into a Nafion® matrix and crosslinked with glutaraldehyde by a one-pot reaction in buffered solution, producing a stable BOD-based biogel. The biogel provides stable electrode performance and allows the direct electron-transfer mechanism of multicopper centers buried in the enzyme. A biocatalytic reduction current of −1.52 ± 0.24 mA cm−2 at 0.19 ± 0.06 V was observed under gas diffusion conditions. Additionally, the bioelectrode showed unprecedented long-term stability under continuous operation combined with satisfactory catalytic current without redox mediator. The BOD-based biogel layer thickness and the entrapment of BOD into Nafion network are crucial for the biocathode stability, and BOD crosslinking by glutaraldehyde contributes to enhance the catalytic currents. Further, the BOD-based biogel provides a suitable microenvironment for long-term enzymatic activity involving three-phase interfacial reaction. The present study provides new insights into enzyme immobilization to overcome the critical short-term stability of enzyme-based electrochemical devices for practical applications.

Nos processos eletroquímicos existem diferentes tipos de materiais e técnicas que podem ser utilizados para a realização de experimentos. Basicamente a principal característica para a esses materiais é a condutividade elétrica. Devido a essa propriedade estar presente nos metais, estes apresentam destaque, uma vez que a possibilidade de realizar modificações ou apenas utilizar o elétron como reagente já torna possível o uso das técnicas eletroquímicas. O conhecimento e domínio dos diversos tipos de materiais e técnicas leva a produção de novos sensores, que podem ser padronizados visando sua reprodutibilidade. Devido ao sistema ser de fácil utilização, os sensores tem se tornado uma ferramenta útil, sendo a sensibilidade e seletividade características essenciais para os mesmos. Diante do exposto, este trabalho visou utilizar poliestireno, que é um polímero não condutor, porém de baixo custo, como aglutinante para folhas de grafite, que é um material com propriedades condutivas. Essa mistura foi testada em várias proporções, tendo como principais resultados materiais eletródicos na forma de disco, contendo 80 ou 85% de folhas de grafite. Foi realizado polimento mecânico na superfície deste material e, em seguida, polimento eletroquímico por voltametria cíclica em ácido sulfúrico, visando homogeneização da superfície e retirada de impurezas. Testes de evaporação do solvente foram efetuados visando decréscimo de resistência elétrica do material, utilizando-se uma sonda aniônica de ferrocianeto/ferricianeto de potássio para avaliação da transferência eletrônica e estudos de reversibilidade, os quais demonstraram resultados satisfatórios. As caracterizações morfológicas do material foram feitas através de MEV, TGA e DSC. Após estes estudos, o material eletródico foi utilizado para incorporação de uma sonda de DNA e detecção do alvo complementar, visando sua aplicabilidade como bioeletrodo, sendo observado diferenciação representativa entre os sinais eletroquímicos de sonda e alvo. In electrochemical processes there are different types of materials and techniques that can be used to carry out experiments. Basically, the main resource for these materials is electrical conductivity. Consider this property to be present in metals, these highlights, since it is possible to make changes or just use the electron as a reagent already makes it possible to use electrochemical techniques. The knowledge and mastery of different types of materials and techniques leads to the production of new sensors, which can be standardized using their reproducibility. Accept the user-friendly system, the sensors are made a useful tool, with sensitivity and the selection of characteristics essential for them. In view of the above, this work uses polystyrene, which is a non-conductive polymer, but low cost, as a binder for graphite sheets, which is a material with conductive properties. This mixture was tested in various proportions, with the main results being electronic materials in the form of discs, containing 80 or 85% graphite sheets. Mechanical polishing was carried out on the surface of this material and then electrochemical polished by cyclic voltammetry in sulfuric acid, using the homogenization of the surface and the removal of impurities. Evaporation tests of the solvent were carried out with a reduction in the electrical resistance of the material, using an anionic potassium ferri/ferrocyanide probe to evaluate the electronic transfer and reversibility studies, which demonstrated satisfactory results. As morphological characterizations of the material were made through SEM, TGA and DSC. After these studies, the electronic material was used for the incorporation of a DNA probe and the detection of a complementary target, applying its applicability as a bioelectrode, being observed the representative difference between the electrochemical signals of probe and target. Dissertação (Mestrado) 2022-02-28

Made available in DSpace on 2018-12-11T17:14:23Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-10-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) We report on the photoelectrocatalytic degradation of the endocrine disruptor propyl paraben (PPB) using a TiO2 nanotube (TiO2-NT) electrode prepared via chemical anodization, and a TiO2-NT electrode modified with WO3 by electrodeposition. Solutions containing 50 mg L− 1 PPB were subjected to the photoelectrocatalytic process in a 0.2 L one-compartment electrochemical cell under UV/VIS irradiation, and the effects of bias potential (+ 0.5, + 1.0 and + 1.5 V) and solution pH (3.0, 7.0 and 10) on the performances of the unmodified and modified electrodes were investigated. Scanning electron micrographs (SEM) showed that the nanotubes were highly organized and perpendicularly aligned with a mean length of 800 nm. According to energy dispersive X-ray and SEM analyses, the concentration of W in the TiO2-NT/WO3 electrode was ~ 0.75% and the distribution of the modifier was continuous and homogeneous on the surface, with pores uncovered and decorated with WO3. The photocurrent of the TiO2-NT/WO3 electrode was improved by more than 20% in relation to its unmodified counterpart. The maximum degradation efficiencies were achieved at higher applied potentials and under acidic conditions for both electrodes. However, best results were obtained using the TiO2-NT/WO3 electrode with an applied potential of + 1.50 V and at pH 3. Under these conditions, more than 99% of PPB was removed in 30 min and 94% mineralization was achieved in 60 min. The photoactivity of the electrode was highly stable even after exhaustive application, indicating that WO3 deposition is an important method for improving the properties of TiO2-NT electrodes as applied to organic oxidation. Instituto de Química de São Carlos Universidade de São Paulo Instituto Nacional de Tecnologias Alternativas para Detecção Avaliação Toxicológica e Remoção de Micropoluentes e Radioativos (INCT-DATREM) Instituto de Química Unesp Instituto Nacional de Tecnologias Alternativas para Detecção Avaliação Toxicológica e Remoção de Micropoluentes e Radioativos (INCT-DATREM) Instituto de Química Unesp FAPESP: #2013/08543-3 FAPESP: #2014/50945-4 FAPESP: #2016/01937-4 CNPq: 301492/2013-1 CNPq: 465571/2014-0

The influence of different supporting electrolytes as well as of different current densities on RO16 dye electrochemical oxidation using BDD electrodes has been systematically studied. The RO16 azo-dye electrooxidation experiments were performed at different current densities and three different supporting electrolytes: H2SO4 0.1 mol L-1, HClO4 0.1 mol L-1 and K2SO4 0.1 mol L-1. The results showed that a higher degradation for reactive azo dye RO16 was observed for the K2SO4 (pH=10) supporting electrolyte for a current density of 100 mA cm-2. This behavior can be associated with the deprotonation effect of the dye molecule, which can facilitate breakdown of the molecule, specifically the azo bond making color removal more efficient. In addition, in this pH there is a greater amount of hydroxyl ion (OH-) available increasing the hydroxyl radical formation.

A graphite-polyurethane composite electrode (GPUE) was modified by electrodeposition of copper nanoparticles (CuNP) followed by electrochemical treatment in NaOH (GPUE-CuNP), in order to prepare an amperometric sensor for the determination of cysteine (Cys). Cyclic votammograms of Cys solutions at GPUE-CuNP allowed the description of a sequence of electrochemical reactions involving Cys oxidation and Cu/Cu+ equilibrium, generating a stable Cys-Cu+ complex. The presence of these nanoparticles was confirmed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) data. Hence, the developed device was then used as a Cys amperometric flow detector in a wall-jet system, after evaluation of flow injection parameters in an undescribed approach. In this system, a limit of detection (LOD) of 4.24 µmol L-1 was obtained with an analytical frequency of 36 determinations h-1. Intra-day and inter-day reproducibility and repeatability of the modified surface was evaluated. Then the GPUE-CuNP performance was investigated in the determination of Cys content in food supplements. Interference tests were carried out with pyridoxine, ascorbic acid, tryptophan and SO4 2- ions. The main interference was attributed to the interaction of some of these substances with copper oxides.

Orientadora: Profa. Dra. Lucimara Stolz Roman Dissertação (mestrado) - Universidade Federal do Paraná, Setor de Ciências Exatas, Programa de Pós-Graduação em Física. Defesa: Curitiba, 18/02/2020 Inclui referências Resumo: Poli(3,4-etilenodioxitiofeno):poli(estireno sulfonado), PEDOT:PSS, é um compósito polimérico capaz de substituir o óxido de índio dopado com estanho (ITO) como eletrodo transparente em dispositivos eletrônicos. No entanto, os filmes de PEDOT:PSS apresentam condutividades com duas ordens de grandeza a menos que o ITO, fato que se apresenta como um grande desafio na busca por dispositivos orgânicos livres do ITO. Apesar do PEDOT ser um bom condutor, os filmes de PEDOT:PSS normalmente não conseguem explorar todas as propriedades elétricas do PEDOT pelo fato de apresentar PSS em sua composição. O PSS é um polímero isolante, adicionado para promover estabilidade da dispersão em água. A fim de aumentar a performance elétrica do PEDOT e superar as limitações isolantes, o presente trabalho propõe a utilização de filmes finos feitos do material compósito de óxido de grafeno (GO) e PEDOT:PSS em uma dispersão aquosa, seguido de um tratamento com etilenoglicol (EG) nos filmes secos. Observa-se um aumento de duas ordens de grandeza nos valores de condutividade, bem como os aumentos significativos na transmitância na região do espectro visível, e na hidrofobicidade dos filmes, decorrentes da retirada do PSS. Além disso, foi investigada a estabilidade mecânica dos filmes em um substrato de PET através de ciclos de torção e medidas elétricas. A razão mássica ótima para esse compósito é de 0,058 de GO/PEDOT, promovendo maior condutividade elétrica pelo fato das cadeias do PEDOT se orientarem de melhor forma, provado pelos espectros das espectroscopias de Auger Ressonante e NEXAFS. O tratamento com EG remove parte do PSS dos filmes, diminuindo tanto a rugosidade quanto a espessura, razões essas que contribuem com o aumento da condutividade e transmitância. Medidas em baixa temperatura foram realizadas e o modelo de Mott VRH foi aplicado, mostrando que a condução ocorre em 3 dimensões (3D) e que o tratamento com solvente aumenta a condutividade característica e diminui a energia de ativação de hopping, não alterando a temperatura característica. Isso indica que o tratamento com EG promove a diminuição do tempo de transferência de carga e resistividade. Palavras-chave:PEDOT:PSS. Óxido de Grafeno. Eletrodo. Transmitância. Condutividade. Estabilidade. Flexibilidade. Ordenamento. Abstract: Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS, is a polymeric composite that can substitute indium tin oxide (ITO) as transparent electrode in electronic devices. However, PEDOT:PSS films have conductivities two orders of magnitude lower than ITO, which is still the main challenge in the achievement of ITO-free organic devices. Even PEDOT being a good conductor, PEDOT:PSS films have not the full electrical performance of PEDOT because of PSS, an insulator polymer added to provide water solubility. To enhance PEDOT electrical performance and overcome the insulator limitations, we prepared thin films based on graphene oxide (GO) aqueous dispersion and PEDOT:PSS solution by drop casting this mixture on substrates followed by a treatment on dried films with ethylene glycol (EG). An increment of two orders of magnitude in conductivity values was observed as well as increase in transmittance at visible region and in hydrophobicity of GO:PEDOT:PSS thin films due to partial removal of PSS. It was further investigated the films mechanical stability on PET substrates by torsion cycle and electrical measurements. Mass ratio equal to 0.058 of GO/PEDOT provides higher electrical conductivity due to higher chains orientation of PEDOT probed by NEXAFS and Resonant Auger Spectroscopy measurements, and EG treatment also decreased the roughness and thickness of thin films, which promoted increment in conductivity and light transmittance. Low temperature electrical measurements and application of Mott Variable Range Hopping (VRH) model showed that the conduction occurs in three dimensions (3D) and the solvent treatment increases the characteristic conductivity and decreases the activation hopping energy, remaining almost unchanged the characteristic temperature. It indicates that EG treatment promotes a decrease in charge transfer time and resistivity. Keywords:PEDOT:PSS. Graphene Oxide. Electrode. Transmittance. Conductivity. Stability. Flexibility. Ordering.

Made available in DSpace on 2020-12-12T02:00:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-01-01 This paper describes a voltammetric study of cadmium nitroprusside synthesized from different compositions of water/formamide in your reaction of Cd2+ with [FeIII(CN)5NO]2- (CdNP). After infrared and transmission electron microscopy characterization, the CdNP was incorporated into a carbon paste electrode and a systematic voltammetric study was performed for four systems (CdNP-1, CdNP-2, CdNP-3 and CdNP-4). The spectroscopic studies reveals that all preparations was conducted with success. The cyclic voltammogram of all CdNP particles obtained from a carbon paste electrode modified (10% m/m) exhibited a redox couple with formal potential (Eθ') = 0.63 ± 0.02 V (10 % (m/m); v=20 mV s-1; KNO3 1.0 M) attributed to the redox process [FeII(CN)5NO]/[FeIII(CN)5NO] in the presence of Cd2+. São Paulo State University (Unesp) School of Engineering Department of Physics and Chemistry, Campus of Ilha São Carlos Institute of Physics University of São Paulo Institute of Education Science and Technology of Goiás, Campus of Valparaíso School of Chemical Sciences Dublin City University São Paulo State University (Unesp), Campus of Rosana Department of Fundamental Chemistry Institute of Chemistry University of São Paulo São Paulo State University (Unesp) School of Engineering Department of Physics and Chemistry, Campus of Ilha São Paulo State University (Unesp), Campus of Rosana

Biomass comprises an attractive source of carbon materials for energy conversion and storage applications, because it provides a low cost and sustainable approach for the production of carbon-based electrode materials at large scale. Here, we demonstrate the preparation of a three-dimensional and hierarchical carbon foam (3DCF) from bio-renewable Pinus nigra pine, using a chemical degradation method followed by two simple carbonization steps in presence of argon gas. The as-prepared 3DCF in supercapacitor electrode shows high scan rate capability up to 10 V s−1, specific capacitance of 165 F g−1 at the specific current of 3.3 A g−1 in 6 M KOH electrolyte in three-electrode cell configuration, and retains 69.6% of its initial capacitance when the specific current increased to 13.3 A g−1. Furthermore, a 3DCF based symmetrical two-electrode cell has been constructed that shows a satisfactory specific energy of 6.6 Wh kg−1 at specific power of 2.3 kW kg−1, and maintains the specific energy of about 50% at high specific power of 7.3 kW kg−1 under an operating voltage of 1.4 V in 2 M LiClO4 aqueous electrolyte. These results reveal a sustainable and low-cost electrode fabrication at large quantity for fabricating high performance supercapacitors with both KOH and Li-ion based electrolytes.

We investigate how Li intercalation into composite electrodes resulting from the combination of graphitic carbon felt (CF) with carbon nanotubes (CNTs) functionalized with electroactive nanoparticles (NPs) depends on NP concentration. To this end, we study CF electrodes coated or not with hydrophilic CNTs containing electrodeposited β/γ-MnO2NPs (wt% 25, 42, and 69) with hollow-nanotube structure. Galvanic coupling between the CNTs and the NPs is the reason why the electrochemical performance of CNT-NP nanocomposites varies with the NP concentration. The CNT coating on the CF electrode also avoids capacity fading of the CF/MnO2NP electrodes and prevents carbon fibers from interconnecting with SEI. More specifically, the CNTs stabilize the solid electrolyte interphase and prevent NP detachment, thereby producing electrodes with long-term cyclability. The best electrochemical performance occurs for CNT/MnO2NP mass wt% 25 (1114 mAh g−1, 1st discharge/charge Faradaic efficiency ~80% at 1 A g−1, cut-off potential = 4–0.005 V vs Li+/Li).

Um método foi desenvolvido para a determinação e especiação de Cr(III) e Cr(VI) baseado na utilização de um eletrodo de pasta de carbono modificado com sílica gel funcionalizada com 1,5-difenilcarbazida. A primeira parte deste trabalho envolveu a modificação da sílica gel com 3-aminopropiltrietoxisilano, seguida do acoplamento com glutaraldeído e funcionalização com 1,5-difenilcarbazida (DFCI). Esse material foi misturado com grafite em pó e óleo mineral para a preparação do eletrodo de pasta de carbono modificado (EPCM) A determinação de Cr(VI) envolveu a pré concentração dessa espécie no EPCM através do complexo Cr(III)-difenilcarbazona, Cr(DFCO)3+, o qual é formado da reação entre Cr(VI) e DFCI no EPCM. A retenção do complexo Cr(DFCO)3r no EPCM foi investigado por voltametria cíclica em função do tempo de acumulação e da concentração de Cr(VI) na solução, em ácido sulfurico 0,05 mol L'1 como eletrólito suporte. A corrente de pico catódica em potencial próximo de -0,45 V vs Ag/AgCl (KC1 3 mol L’1) foi proporcional à concentração de Cr(VI) na solução, na faixa de concentração de 2x10'8 a 2x10'7 mol L’1. Um desvio padrão relativo (10 replicatas) de 6,7% foi obtido na determinação de Cr(VI) 3,2xl0‘8 mol L’1 com o EPCM, com um limite de detecção de 1,7x10’9 mol L’1. O Cr(III) foi determinado pela diferença entre as quantidades de Cr(VI) total e Cr(VI), após oxidação de Cr(III) a Cr(VI) com KMnCU, em meio ácido. O Eletrodo de pasta de carbono modificado foi empregado na determinação de Cr(III) e Cr(VI) em efluentes de curtumes aplicando o método da adição de padrão e os valores obtidos apresentaram boa concordância com os obtidos pelo método espectrofotométrico padrão. A new method has been developed in this work for the determination and speciation of the Cr(III) and Cr(VI) based on the use of a modifíed carbon paste electrode with silica gel functionalized with 1,5-diphenylcarbazide. The first part of this work involved the modification of the silica gel surface with 3-aminopropyltriethoxysilane, followed by the coupling with glutaraldehyde and functionalization with 1,5-diphenylcarbazide (DPCI). This material was mixed with powder graphite and mineral oil for the preparation of the modifíed carbon paste electrode (MCPE). The Cr(VI) was preconcentrated on the MCPE by Cr(III)-diphenycarbazone complex, Cr(DFCO)3+, that is formed from the reaction of Cr (VI) with DFCI on the MCPE. The retention of Cr(DFCO)3+ on MCPE has been investigated by cyclic voltammetric technique in function to the accumulation time and Cr(VI) concentration in the aqueous solution, using 0.05 mol L’1 H2SO4 as supporting electrolyte. The cathodic peak current at potencial near to -0.45 V vs Ag/AgCl (KC1 3 mol L'1) was proporcional to the Cr(VI) concentration over 2x10'8 to 2x10'7 mol L’1 range. The relative standard desviation (10 replicates analysis) at the 3.2x10’ mol L’ of Cr(VI) was 6.7% and the detection limit of the MCPE to Cr(VI) was 1.7 xlO’9 mol L’1. The Cr(III) has been determined by diference between total Cr(VI) and Cr(VI), after oxidation to Cr(VI) by KMnO4, in acid media. The developed method has been applied to the determination of chromium speciation in tannery effluents by using the standard addition method and the Cr(VI) and Cr(III) concentrations obtained are in agreement with those obtained by standard spectrophotometric method. Dissertação (Mestrado)

CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico FAPEMIG - Fundação de Amparo a Pesquisa do Estado de Minas Gerais O presente trabalho descreve a síntese e caracterização de filmes nanocompósitos formados entre hexacianoferrato de zinco e nanotubos de carbono (HCFZn/NTC) e hexacianoferrato de zinco e óxido de grafeno reduzido (HCFZn/OGr), com posterior aplicação desses materiais como eletrodos em baterias de íons zinco. A síntese dos filmes nanocompósitos foi realizada de acordo com o método interfacial utilizando soluções dos reagentes precursores (ZnCl2, K3[Fe(CN)6]) que foram adicionadas em dispersões dos nanomateriais de carbono previamente preparadas, originando a autodeposição de filmes na interface do sistema. Os resultados revelaram que todos os compostos apresentam estrutura cristalina, com a presença de uma única fase de estrutura romboédrica para os filmes de HCFZn puro e HCFZn/OGr. Porém, para o filme HCFZn/NTC também foi observado a presença de uma fase secundária associada a estrutura ortorrômbica. Dados espectroscópicos mostraram tanto a presença do hexacianoferrato de zinco como dos nanomateriais de carbono no filme, e as imagens de microscopia eletrônica de varredura comprovaram a interação desses nanomateriais, sendo possível ainda observar mudanças no tamanho e morfologia das partículas de acordo com a estrutura de carbono utilizada. Os filmes HCFZn e HCFZn/NTC foram aplicados como materiais catódicos em baterias de íons zinco. Os resultados revelaram que o filme HCFZn/NTC exibiu uma capacidade específica de 25,81 mA h g-1 e retenção de 55,77 % após 200 ciclos, valores muito superiores aos obtidos para o filme que continha apenas HCFZn. Desse modo, a boa reversibilidade a uma alta diferença de potencial apresentada pelo filme HCFZn/NTC, torna possível o aperfeiçoamento e desenvolvimento de dispositivos de armazenamento de energia translúcidos, flexíveis e leves que possam ser utilizados como uma alternativa de baixo custo, segura e ambientalmente amigável às tecnologias tradicionais. The present work describes the synthesis and characterization of nanocomposite films prepared between zinc hexacyanoferrate and carbon nanotubes (ZnHCF/CNT) and zinc hexacyanoferrate and reduced graphene oxide (ZnHCF/rGO), with subsequent application of these materials as electrodes in zinc ions battery. The synthesis of the nanocomposite films was performed according to the interfacial method using solutions of the precursor reagents (ZnCl2, K3[Fe(CN)6]), that were added in previously prepared dispersions of the carbon nanomaterials, with consequent spontaneously formation of a film at interface of the system. The results showed that all the compounds have crystalline structure, with the presence of a single rhombohedral structure phase for the films of HCFZn and ZnHCF/rGO films, however, for the ZnHCF/CNT film the presence of a secondary phase associated with the orthorhombic structure was also observed. Spectroscopic data showed the presence of both zinc hexacyanoferrate and the carbon nanomaterials in the film, and the scanning electron microscopy images reveal the interaction of these nanomaterials, being possible to observe changes in the size and morphology of ZnHCF particles according to the carbon structure used. The ZnHCF and ZnHCF/CNT films were applied as cathodic materials in zinc ion batteries. The results showed that ZnHCF/CNT film exhibited a specific capacity of 25.81 mA h g-1 and retention of 55.77 % after 200 cycles, much higher values than those obtained for the film containing only ZnHCF. In this way, the good reversibility and high potential difference for ZnHCF/CNT film make it possible to improve and develop translucent, flexible and light energy storage devices that can be used as a low-cost, safe and environmentally friendly alternative material to traditional technologies. Dissertação (Mestrado)

Nanostructured capacitive biosensors, combined with inexpensive fabrication technologies, may provide simple, sensitive devices for detecting clinically relevant cancer biomarkers. Herein, we report a novel platform for detecting the pancreatic cancer biomarker CA19-9 using low-cost screen-printed interdigitated electrodes (SPIDEs). The SPIDEs were modified by carbon nano-onions (CNOs) and graphene oxide (GO) films, on which a layer of anti-CA19-9 antibodies was immobilized. The modification with CNOs and GO significantly improved the analytical performance of the biosensor, which displayed superior results to those prepared only with GO. The biossensor exhibited high reproducibility and a relatively low limit of detection of 0.12 U mL-1. Using these devices in combination with information visualization methods we were able to detect CA19-9 in whole cell lysates of colorectal adenocarcinoma. The fabrication of these low-cost, disposable immunosensors is a successful attempt to explore CNOs in capacitive biosensors, which may be extended for detection of different cancer biomarkers., CAPES (001), CNPq, INEO and FAPESP (2012/15543-7, 2013/14262-7, 2015/01770-0, 2016/00991-5 and 2017/12096-3). M.N.C is grateful for the economic support from Vicerrectoria de Investigaciones and the Centro de Excelencia en Nuevos Materiales (CENM) from the Universidad del Valle.

Made available in DSpace on 2019-10-04T12:15:42Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-09-01. Added 1 bitstream(s) on 2021-07-15T15:04:47Z : No. of bitstreams: 1 S0103-50532019000901964.pdf: 981725 bytes, checksum: b595a9a0fb7fce0f220260e9cc6193f6 (MD5) Universidade Federal do ABC (UFABC) Multiuser Central Facilities (UFABC) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Ab'Saber Group PROQUALIS-IFMA In this work, the gas diffusion electrode (GDE) cathode of Vulcan XC72 carbon modified with nanoparticles of WO2.72 (WO2.72 / Vulcan XC72) was used for H2O2 electrogeneration and degradation of 350 mL of Orange II (OH) and Sunset Yellow FCF (SY) azo dyes by electro-Fenton (EF) and photoelectro-Fenton (PEF) processes with different Fe2+ initial content (1.00, 0.50 and 0.25 mmol L-1). The WO2.72 / Vulcan XC72 GDE electrolyzed approximately 3 times more H2O2 than the Vulcan XC72 GDE. Decolorizations and mineralizations of the dye solutions were more efficient at higher concentrations of Fe2+. The decolorization decay showed pseudo-first-order kinetics. The most promising decolorization results obtained at processes of WO2.72 / Vulcan XC72 cathode combined with Pt anode (100% color removal of OII and SY at 30 and 20 min of electrolysis with 1.00 mmol L-1 Fe2+, respectively). The best mineralization achieved in trials of WO2.72 / Vulcan XC72 cathode combined with boron-doped diamond (BDD) anode (82% total organic carbon (TOC) removal of OII by PEF / 1.00 after 3 h and 90% TOC removal of SY by PEF / 050 after 4 h). It was found that SY decolorization was faster and mineralization showed a similar yield independent of oxidized dye. Univ Fed ABC UFABC, LEMN, CCNH, Rua Santa Adelia 166, BR-09210170 Santo Andre, SP, Brazil Inst Fed Educ Ciencia & Tecnol Maranhao IFMA, Campus Acailandia,R Projetada S-N, BR-65930000 Acailandia, MA, Brazil Univ Sao Paulo, IQSC, CP 780, BR-13566590 Sao Carlos, SP, Brazil Univ Estadual Paulista Julio de Mesquita Filho Un, Inst Nacl Tecnol Alternat Deteccao Avaliacao Toxi, Inst Quim, BR-14800900 Araraquara, SP, Brazil Univ Estadual Paulista Julio de Mesquita Filho Un, Inst Nacl Tecnol Alternat Deteccao Avaliacao Toxi, Inst Quim, BR-14800900 Araraquara, SP, Brazil FAPESP: 2015/10314-8 FAPESP: 2016/00819-8 FAPESP: 2017/21846-6 FAPESP: 2017/22976-0 FAPESP: 2017/26288-1 FAPESP: 2017/10118-0 CNPq: 406612/2013-7 CNPq: 429727/2018-6

The objective of this work was to assess the performance of an antimony ion-selective electrode (ISE) sensor system, using manual and automatic operating modes, for measuring the potential of hydrogen (pH), in real time, in Oxisols with different characteristics. Samples were manually collected and sent to a laboratory for determination of pH in water and calcium chloride, whose values were used as references. Another set of samples was also automatically collected using a commercial equipment, and readings were performed in manual mode. The performance parameters of the sensor system were calculated and evaluated. Part of the soil samples was used to assess the degree of influence of moisture in determining pH. Calibration lines were constructed. The statistical analysis revealed better results for the manual mode. Both modes of operation had errors superior to those accepted as a limit in laboratory techniques, however, with the possibility of high data density and with positive and promising results. Soil moisture interfered with the result of the readings. The sensor system yields a sampling density of 45 data per hectare, which represents a great contribution to the intensification of data for a better spatial evaluation of soil information. Resumo: O objetivo deste trabalho foi avaliar o desempenho de um conjunto sensor direto, de íon seletivo (ISE) de antimônio, usando os modos de funcionamento manual e automático, na determinação do potencial hidrogeniônico (pH), em tempo real, em Latossolos com diferentes características. Amostras foram coletadas com trado e encaminhadas a laboratório para a determinação do pH em água e do cloreto de cálcio, cujos valores foram utilizados como referência. Um segundo conjunto de amostras foi coletado automaticamente utilizando-se um equipamento disponível no mercado, e foram executadas leituras em seu modo manual. Parâmetros de desempenho do conjunto foram calculados e avaliados. Parte dessas amostras de solo foi utilizada para avaliar a influência da umidade na determinação do pH. Retas de calibração foram construídas. As análises estatísticas apresentaram melhor resultado para o modo manual. Ambos os modos de operação apresentaram erros superiores aos aceitos como limite em técnicas laboratoriais, porém, com a possibilidade de elevada densidade de dados e com resultados positivos e promissores. Verificou-se que a umidade do solo interferiu no resultado das leituras. O conjunto sensor fornece uma densidade de amostragem de 45 dados por hectare, o que representa uma grande contribuição para a intensificação de dados para melhor avaliação espacial da informação do solo.

A composite electrode based on graphite oxide (GrO)-polyurethane (PU) modified with β-cyclodextrin (CD) was proposed for the simultaneous determination of three drugs: terbutaline (TER), nimesulide (NIM), and methocarbamol (MET), as possible contaminants in river water samples. To evaluate the performance of the proposed CD-GrOPUE, voltammetric techniques were used and two other electrodes were fabricated (GrOPUE and GrPUE) for comparison. The functionalization of the GrO was confirmed by scanning electron microscopy images, energy-dispersive X-ray spectroscopy analysis, and thermogravimetry. Cyclic voltammograms obtained for TER, NIM, and MET indicated an irreversible behaviour at 0.6 V, 0.9 V and 1.2 V (vs. Ag/AgCl (3 mol L−1 KCl)), respectively, on each working electrode, with the highest peak current values been obtained using the CD-GrOPUE. Under optimal conditions, using square-wave voltammetry, the linear ranges obtained (and limit of detection) for TER, NIM, and MET were 2.5–30 (0.55), 0.62–7.3 (0.083), and 0.62–7.3 (0.077) μmol L−1, respectively. The analytical method developed were applied in the simultaneous determination of TER, NIM, and MET in river water samples, with results like those obtained using a reference spectrophotometric method (at a confidence level of 95%). One can conclude, that the modification of GrO with CD arrays made possible the development of a robust and simple sensor platform for environmental analyses.

Made available in DSpace on 2018-12-11T16:58:02Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-10-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Fundação para a Ciência e a Tecnologia Abstract Modified electrodes based on films of Schiff base complexes are excellent candidates for sensing applications. The influence of the electrode material, glassy carbon, platinum, gold or indium tin oxide, on the electrodeposition of nickel-N,N'-bis(salicylidene)-1,3-propanediamine (Ni-Salpn) films in 1,2-dichloroethane (DCE) was investigated, and their electrochemical behaviour was evaluated by cyclic voltammetry and electrochemical impedance spectroscopy. The effect of the electrodeposition potential and electrodeposition time on the electrochemical behaviour of Ni-Salpn was examined using glassy carbon as substrate. The film growth process was investigated using the electrochemical quartz crystal microbalance and UV-vis absorption spectroscopy and structural differences between the Ni-Salpn complex and the Ni-Salpn film were examined by micro-Raman spectroscopy. The results demonstrate that the electrodeposition mechanism is independent of the electrode material, but that the nature of the substrate material influences the rate of film growth, the electrochemical behaviour and the stability of the film-modified electrodes in aqueous solution. Counteranion insertion during oxidation can break the bonds between the complexes in the stacked Ni-Salpn film structure and cause both mass loss and blockage of the redox metal centre activity, but these effects are small in thin films. Departamento de Física, Química e Biologia, Faculdade de Ciências e Tecnologia, UNESP Univ Estadual Paulista Department of Chemistry, Faculty of Sciences and Technology, University of Coimbra Instituto de Química de São Carlos, Universidade de São Paulo Departamento de Física, Química e Biologia, Faculdade de Ciências e Tecnologia, UNESP Univ Estadual Paulista FAPESP: 2012/25140-7 FAPESP: 2013/22087-0 Fundação para a Ciência e a Tecnologia: SFRH/BPD/46635/2008

Trata-se de um estudo baseado em análise documental de monografias, artigos técnicos e revistas especializadas sobre o processo de soldagem subaquática molhada conhecida como soldagem subaquática úmida muito utilizada na área offshore. O objetivo desse estudo é ter uma visão geral do processo de soldagem subaquática úmida com a utilização da técnica com eletrodos revestidos. Várias abordagens são descritas nesse trabalho uma vez que o processo de soldagem subaquática tem como elemento principal o profissional qualificado para a utilização da técnica. Nesse trabalho são citadas as variáveis do processo, limitações de profundidade, que é um caso de preocupação constante, os efeitos ambientais sobre o processo, soldas e técnicas de inspeção subaquáticas para garantir a qualidade da solda, ou seja, que o resultado final seja soldas isentas de defeitos.

In a modern world where efficiency, precision and time savings have been prioritized, a new frontier has been seen in the biosensors to be explored. A potential alternative to the current means of quantification and qualification, the biosensors have been gaining more and more prominence as they are devices of quantification and qualification cheaper and simple, when compared with the current techniques and with the advantage of being able to be used many times in the place where the sample is collected. According to its application is produced by different methods, in which it has in its basic constitution a sensor element of biological origin, an inorganic half-conductor used as a transducer and a signal processing device. In this article we show the scientific production involving biosensors, together with their synthesis method, which differs according to their application in order to detect the most varied analytes, chemical species and even living organisms.

Em um mundo moderno onde cada vez mais se tem priorizado a eficiência, precisão e economia de tempo, tem-se visto nos biossensores uma nova e longa fronteira a ser explorada. Uma alternativa em potencial aos meios de quantificação e qualificação atuais, os bionssensores vem ganhando cada vez mais destaque por serem dispositivos de quantificação e qualificação mais baratos e simples, quando comparados com as técnicas atuais e com a vantagem de poder ser utilizado muitas vezes no local onde a amostra é coletada. De acordo com sua aplicação é produzido por diferentes métodos, na qual tem em sua constituição básica um elemento sensor de origem biológica, um semi-condutor inorgânico utilizado como transdutor e um dispositivo de processamento de sinal. Neste artigo é mostrado a produção científica que envolve biossensores, juntamente com seu método se síntese, que difere de acordo com sua aplicação, afim de detectar os mais variados analitos, espécies químicas e até mesmo organismos vivos.

Mestrado em Engenharia Física Este trabalho tem como objetivo a síntese de elétrodos à base de grafeno induzido por laser (LIG) para serem explorados pela primeira vez num sistema de desionização capacitiva (CDI) para remoção de iões da água. O trabalho foi desenvolvido em colaboração com a Bosch Termotecnologia S.A. Aveiro no âmbito de um projeto em Co-promoção. A síntese dos elétrodos de LIG foi realizada utilizando um polímero comercial, Kapton, sobre o qual se fez incidir um feixe laser de CO2. O trabalho focou-se no estudo da influência de vários parâmetros de processamento a laser para a otimização dos elétrodos. A caracterização do material foi feita usando as técnicas de microscopia eletrónica de varrimento (SEM), medição da superfície específica (BET), espectroscopia de Raman, medidas de resistência elétrica pela técnica de Van der Pauw e testes de estabilidade em fluxo de água. Paralelamente a este estudo foram também caracterizados quatro elétrodos comerciais. Para a caracterização dos elétrodos foi desenvolvido um sistema que permite avaliar o comportamento no processo de desionização capacitiva nos modos de corrente (CC) e tensão (CV) constantes. O desempenho do material desenvolvido foi avaliado através da análise de ciclos de carga/descarga, e comparado com o comportamento dos dois melhores elétrodos comerciais. Os testes realizados permitiram observar a operação de CDI em todos os elétrodos, embora com diferentes níveis de desempenho. Os elétrodos de LIG revelaram uma curva de carga/descarga tipicamente capacitiva, não obstante o seu desempenho ser inferior aos elétrodos comerciais. Os resultados obtidos neste estudo exploratório, aliados ao método de produção a laser de baixo custo, põem em evidência o potencial destes elétrodos para uma aplicação CDI industrial requerendo, no entanto, a sua otimização. The goal of this work is the synthesis of electrodes based on laser induced graphene (LIG) to be explored for the first time in a capacitive deionization (CDI) system for ion removal from water. The work was developed in cooperation with Bosch Thermotechnology S.A Aveiro in the ambit of a project in Co-promotion. The LIG’s electrodes synthesis was done using a commercial polymer, Kapton, in which a CO2 laser beam was irradiated. The work focused on the study of the influence of various laser processing parameters for the optimization of the electrodes. The characterization of the material was done using techniques such as scanning electron microscopy (SEM), specific surface adsorption measurements (BET), Raman spectroscopy, Van der Pauw electrical resistance sheet measurements and stability tests in the presence of a water flow. In parallel with this study, four commercial electrodes were also characterized. For the characterization of the electrodes was developed a system which allowed to evaluate their behaviour in the process of capacitive deionization in the operation modes of constant current (CC) and voltage (CV). The performance of the developed material was assessed via the analysis of the charge/discharge cycles, and comparing them to the behaviour of two other commercial electrodes. The test executed showed the CDI operation in all of the electrodes, although with different levels of performance. The LIG electrodes revealed a charge/discharge curve typically capacitive, regardless of showing inferior performance results compared to the commercial electrodes. The results obtained in this exploratory work, allied to the LIG’s electrode production at low cost, evidences the potential of these electrodes for an industrial CDI application requiring, however, further optimization.

Dissertação submetida como requisito parcial para obtenção do grau de Mestre em Engenharia de Produção As nanopartículas de magnetite e nanoplaquetas de magnetite e hematite foram sintetizadas através do método de co-precipitação com o uso da amónia como agente alcalino e também foi feito um tratamento térmico às nanopartículas de magnetite, a fim de as oxidar e transformar em maghemite. A caracterização físico-química e a morfologia analisadas indicaram que as partículas são cristalinas, sem impurezas e com um diâmetro médio de 12,4 nm para as nanopartículas de magnetite e um diâmetro de 31,3 nm para as nanoplaquetas de magnetite e hematite. Foram estudados os elétrodos fabricados com as nanopartículas em duas gamas de potencial, conseguindo-se valores de capacidade elétrica específica de 77,5 F/g para o elétrodo de magnetite, 43,14 F/g para o elétrodo de magnetite e hematite e de 42,36 F/g para o elétrodo de maghemite, na janela de potencial positivo, a uma velocidade de varrimento de 10 mV/s. A densidade de carga obtida foi de 124,1 mC/cm2 para a magnetite, 62,12 mC/cm2 para a magnetite e hematite e 72,87 mC/cm2 para a maghemite, no potencial positivo e no potencial negativo respetivamente. A influência da massa de óxido na capacidade do elétrodo mostrou que o elétrodo se torna mais estável quando a sua massa é igual a 8 mg. Nanoparticles of magnetite and nanoplates of magnetite and hematite were synthesized by the co-precipitation method with the use of ammonia as an alkaline agent and a thermal treatment was also made to the magnetite nanoparticles in order to oxidize and transform them into maghemite. The physicochemical characterization and morphology analyzed indicated that the particles are crystalline, with no impurities and with an average diameter of 12.4 nm for the nanoparticles of magnetite and a diameter of 31.3 nm for the nanoplates of magnetite and hematite. The electrodes manufactured with the nanoparticles were studied in two potential ranges, obtaining specific capacitance values of 77.5 F/g for the magnetite electrode, 43.14 F/g for the magnetite and hematite electrode and 42.36 F/g for the maghemite electrode in the positive potential window at a scanning rate 10 mV/s. The obtained charge density was 124.1 mC/cm2 for magnetite, 62.12 mC/cm2 for magnetite and hematite and 72.87 mC/cm2 for magnetite, at positive potential and negative potential respectively. The influence of the oxide mass on the electrode capacitance showed that the electrode becomes more stable when its mass is equal than 8 mg.

Gold is among the most used materials in electrocatalysis. Despite this, this noble metal is still too expensive to be used in the fabrication of low cost and disposable devices. In the present work, gold-leaf sheets, usually employed in decorative crafts and wedding candies, is introduced as an inexpensive source of gold. Planar-disc and nanoband gold electrodes were simply and easily manufactured by combining gold leaf and polyimide tape. The planar disc electrode exhibited electrochemical behavior similar to that of a commercial gold electrode in 0.2molL-1 H2SO4; cyclic voltammetry of a 1mmolL-1 solution of potassium ferricyanide (K3[Fe(CN)6]) in 0.2molL-1 KNO3, using this novel electrode, displayed an 80mV difference between the oxidation and reduction peak potentials. The electrode also delivers promising prospects for the development of wearable devices. When submitted to severe mechanical deformation, this electrode exhibited neither loss of electrical contact nor significant variation in electrode response, even after fifteen bending and/or folding cycles. The thickness of the gold-leaf sheet facilitates the production of nanoband electrodes with behavior similar to that of ultramicroelectrodes. The electrode surface is easily renewed by cutting a thin slice off its end with a razor blade; this process led to limiting currents that were reproducible, presenting a relative standard deviation (RSD) of 3.8% (n = 5).

Submitted by Jessica Alves (alves.jessica@ufba.br) on 2018-12-19T16:52:51Z No. of bitstreams: 1 Tese_Jorge Luís Oliveira Santos.pdf: 2465680 bytes, checksum: 8124fb9f472f0ca54cd38fa1dcca7679 (MD5) Approved for entry into archive by Jessica Alves (alves.jessica@ufba.br) on 2018-12-19T16:54:07Z (GMT) No. of bitstreams: 1 Tese_Jorge Luís Oliveira Santos.pdf: 2465680 bytes, checksum: 8124fb9f472f0ca54cd38fa1dcca7679 (MD5) Made available in DSpace on 2018-12-19T16:54:07Z (GMT). No. of bitstreams: 1 Tese_Jorge Luís Oliveira Santos.pdf: 2465680 bytes, checksum: 8124fb9f472f0ca54cd38fa1dcca7679 (MD5) No presente trabalho é reportada a utilização do eletrodo de filme de paládio depositado ex situ sobre amálgama de prata (PdF-AgSAE) como uma nova alternativa para determinação de tálio por voltametria de redissolução anódica. Vários parâmetros experimentais que influenciam a resposta eletroanalítica foram investigados e o PdF-AgSAE foi empregado no desenvolvimento de métodos para determinação de tálio em amostras de água, solos e sedimentos. Na determinação de Tl+ em amostras de águas naturais por voltametria de redissolução anódica com pulso diferencial (DPASV) foi obtida uma faixa linear de trabalho nas concentrações de 3,0 a 100,0 µg L-1 e desvio padrão relativo (RSD) < 2,0%. Os valores de limite de detecção (LD) e limite de quantificação (LQ) foram estimados em 0,89 µg L-1 e 2,96 µg L-1, respectivamente. O PdF-AgSAE também exibiu um bom desempenho analítico na determinação simultânea de Tl+ e Pb 2+ em amostras de água, apresentando correntes de pico bem definidas.

Os cátions metálicos são indispensáveis para muitas das funções vitais do organismo humano e a maioria das doenças estão relacionadas à deficiência de minerais. A alimentação do homem moderno é um fator de perda dos elementos essenciais, pois esses devem ser introduzidos de alguma forma para manter suas quantidades ideais no organismo, já que o corpo humano não pode fabricá-los. Contudo, muitos alimentos de origem vegetal possuem fatores antinutricionais que complexam com nutrientes da dieta humana e interferem na digestão, absorção ou utilização desses e, se ingeridos em altas concentrações, podem diminuir consideravelmente a disponibilidade dos cátions metálicos. Desse modo, o objetivo deste trabalho é avaliar a complexação que ocorre entre os cátions metálicos Cu 2+ , Zn 2+ , Ca 2+ , Mg 2+ e Fe 2+ e compostos presentes na soja (fitatos) e na própolis (compostos fenólicos) utilizando a técnica voltametria. Posteriormente, avaliou-se métodos para descomplexá-los, deixando-os, assim, livres em solução. Em todos os procedimentos experimentais empregou-se a técnica voltametria de pulso diferencial (DPV) e utilizou-se o eletrodo de carbono vítreo (GCE) como eletrodo de trabalho. As variações de intensidade de corrente de pico (I p ) foram analisadas durantes os estudos realizados das soluções dos cátions com eletrólito de suporte (KCl) na ausência e presença da soja e da própolis. Para a matriz soja, verificou-se na complexação dos cátions metálicos, uma competição na contribuição da intensidade de corrente desses cátions e do ácido nítrico. Essa competição inviabilizou o desenvolvimento da metodologia. Já a complexação dos cátions com extrato de própolis ocorreu com todos os cátions analisados. O pH das soluções na ausência e presença de extrato sofreu pequenas alterações, portanto não prejudicou as análises. Verificou-se que o efeito complexante aconteceu em proporções diferentes e as porcentagens de variação das I p das soluções contendo esses cátions na ausência e presença de extrato foram de 42,22% para o cátion Cu 2+ , 99,95% para o Ca 2+ , 77,57% para o Zn 2+ , 97,11% para o Mg 2+ e 85,22% para o Fe 2+ . A utilização do ultrassom e micro-ondas foram avaliados como efeitos descomplexantes. Embora o resultado obtido no tratamento por ultrassom seja melhor, os dois métodos descomplexaram cátions dos compostos do extrato de própolis, e se mostraram eficientes. Nesses estudos de descomplexação com a própolis apenas o cátion Cu 2+ foi analisado, no entanto, é possível aplicar as metodologias para os outros cátions. O método eletroquímico ofereceu as vantagens de ser bastante sensível e rápido, além da simplicidade dos reagentes e equipamentos utilizados, se comparado com os outros métodos instrumentais. The feeding of modern man is a factor of loss of the essential elements, since these must be introduced somehow to maintain their ideal quantities in the organism, once the human body can not manufacture them. However, many foods of plant origin have antinutritional factors, which that complex with nutirents in the human diet and interfere with their digestion, absorption or use and, if ingested at high concentrations, can substantially reduce the availability of metal cations. Thus, the objective of this work is to evaluate the complexation formed between the metallic cations Cu 2+ , Zn 2+ , Ca 2+ , Mg 2+ and Fe2+ and compounds present in soybean (phytates) and propolis (phenolic compounds) using the voltammetry technique. Subsequently, it was evaluated methods to decomplex them, thus leaving them free in solution. In all the experimental procedures, the differential pulse voltammetry (DPV) technique was used and the glassy carbon electrode (GCE) was used as working electrode. The variations of peak current (I p ) were analyzed during the studies of cation solutions with support electrolyte (KCl) in the absence and presence of soybeans and propolis. For the soy matrix, it was verified in the complexation of the metallic cations, a competition in the contribution of the current intensity of these cations and of the nitric acid. This competition impaired the development of the methodology. However, the cation complexation in propolis extract occured with all cations analyzed. The pH of the solutions in the absence and presence of the extract underwent minor alterations, therefore did not affect the analyzes. It was verified that the complexing effect occurred in different proportions and the percentages of variation of the I p of solutions containing these cations in the absence and presence of the extract were 42.22% for Cu 2+ cation, 99.95% for Ca 2+ , 77.57% for Zn 2+ , 97.11% for Mg 2+ and 85,22% for Fe2+. Ultrasonic bath and microwave were evaluated as decomplexing effects. Although the result obtained in the ultrasonic treatment is better, the two methods decomplexed cations of the compounds from the propolis extract, and proved to be efficient. In these studies of decomplexing withpropolis only the Cu 2+ cation was an alyzed, however, it is possible to apply the methodologies to the other cations. The electrochemical method offered the advantages of being very sensitive and fast, besides the simplicity of the reagents and equipment used, when compared with the other instrumental methods.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) A soldagem a arco elétrico por eletrodo revestido (SMAW) é uma das mais antigas técnicas de soldagem e a primeira a ser utilizada industrialmente em grande escala. Durante o século XX a soldagem SMAW foi a mais usada como técnica de união permanente de metais, sendo até hoje, mesmo com coexistência de diversas outras técnicas, uma das que possuem maior utilização no mercado brasileiro. Nesse tipo de soldagem uma das maiores preocupações é o cuidado no armazenamento do eletrodo, pois o mesmo não pode ficar exposto a atmosfera ambiente, já que absorveria umidade, que é danoso para a qualidade da solda. A umidade introduz na zona fundida o hidrogênio que pode levar ao surgimento de trincas a frio. A solução normalmente usada é a da ressecagem em temperaturas até 450º C, acompanhada de armazenamento em estufas, prática que gera custos adicionais para um projeto de fabricação. Nesse contexto o presente trabalho teve a intenção de caracterizar a zona fundida de soldas feitas com eletrodos revestidos E7018 encobertos com filmes de alumínio e PVC, aplicados com o intuito de resguarda-los contra a umidade ambiente, diminuindo custos e tempo com secagem, também variando o valor de aporte térmico utilizado durante a soldagem. Essa atual investigação dá continuidade à pesquisa recente sobre a influência de tais filmes protetores na composição e, em especial, na microestrutura do metal de solda depositado, onde a quantificação dos constituintes e caracterização microestrutural ocorreu através de um software para avaliação de imagens. No presente caso, com a utilização de um microscópio com emissão de campo, MEV-FEG, foram obtidas imagens com elevado contraste, que permitiram um levantamento detalhado dos tipos de constituintes presentes, assim como uma análise mais precisa de sua morfologia. Em particular foi possível avaliar quantitativamente o efeito dos filmes protetores no tamanho de grão e na razão de aspecto do microconstituinte AF (ferrita acicular). Com base numa revisão da literatura é apresentada uma análise crítica acerca dos parâmetros que tiveram maior relevância na formação da microestrutura final e nas propriedades mecânicas obtidas. Os resultados conduziram a constatação de que para maiores valores de aporte térmico a microestrutura, em especial a ferrita acicular, tende a ser mais grosseira. Com a utilização dos revestimentos de PVC e tinta de alumínio obteve-se uma leve diminuição nessa granulometria, já que a microestrutura apresentou-se mais refinada do que com os eletrodos de referência (E7018 puro e BRH4R). The shield metal arc welding (SMAW) is one of the oldest welding processes and the first one to be used in large industrial scale. During the XX century the SMAW was the most applied process for metal joining, remaining until nowadays as one of the most used in the Brazilian market. In this kind of welding one of the biggest problems is to avoid the hydrogen induced cold cracking, what imposes rigid requirements in the storing of the weld consumables. In order to avoid the humidity absorption, the consumables must be dried out in special ovens at temperatures in the order of 450 C, what implies in additional and higher manufacturing costs. In this context a recent research suggested modifications in coating of electrodes providing an alternative for execution of welding with low hydrogen electrode AWS E7018 without having to dry it, The welds were developed with basic coated electrodes (hygroscopic) externally painted with aluminum spray paint for high temperatures or wrapped with thin plastic films (PVC) and aluminum foil films. The induced metallurgical changes in the deposited metal, associated with the addition of new materials to the electrode coating, were investigated, wereby the microconstituents in the fusion zone were quantified using a software for image analysis. In the actual work, with the use of a field emission microscope, MEV-FEG, high contrast images could be obtained, this allowed a detailed characterization of the various microconstituents and a more precise description of their morphology. In special it was possible to evaluate the influence of the protective films in the grain size and aspect ratio of the microconstituent AF (acicular ferrite). On base of a literature review a critical analysis is presented, that embraces the effect of the more relevant parameters on the final microstructure and resulting mechanical properties. The results showed that for higher values of heat input the microstructure, especially the acicular ferrite, tends to be coarser. With the use of PVC coatings and aluminum paint, a slight reduction was achieved in this granulometry, since the microstructure was more refined than with reference electrodes (E7018 pure and BRH4R).

Made available in DSpace on 2020-12-12T01:39:18Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-01-01 Vulcan Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) The objectives of this study were to determine the viability of removing Orange II (OII) dye by simulated solar photoelectro-Fenton (SSPEF) and to evaluate the stability of a WO2.72/Vulcan XC72 gas diffusion electrode (GDE) and thus determine its best operating parameters. The GDE cathode was combined with a BDD anode for decolorization and mineralization of 350 mL of 0.26 mM OII by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF) and photoelectro-Fenton (PEF) at 100, 150 and 200 mA cm−2 and SSPEF at 150 mA cm−2. The GDE showed successful operation for electrogeneration, good reproducibility and low leaching of W. Decolorization and OII decay were directly proportional to the current density (j). AO-H2O2 had a reduced performance that was only half of the SSPEF, PEF and EF treatments. The mineralization efficiency was in the following order: AO-H2O2 < EF < PEF ≈ SSPEF. This showed that the GDE, BDD anode and light radiation combination was advantageous and indicated that the SSPEF process is promising with both a lower cost than using UV lamps and simulating solar photoelectro-Fenton process. The PEF process with the lowest j (100 mA cm−2) showed the best performance-mineralization current efficiency. Centro de Ciências Naturais e Humanas (CCNH) Universidade Federal Do ABC (UFABC), Rua Santa Adélia, 166 Centro de Engenharia Modelagem e Ciências Sociais Aplicadas (CECS) Universidade Federal Do ABC (UFABC), Rua Santa Adélia, 166 Instituto Federal de Educação Ciência e Tecnologia Do Maranhão (IFMA) Campus Açailândia, R. Projetada, s/n Instituto de Química de São Carlos (IQSC) Universidade de São Paulo (USP), Caixa Postal, 780 Instituto Nacional de Tecnologias Alternativas Para Detecção Avaliação Toxicológica e Remoção de Micropoluentes e Radioativos (INCT-DATREM) Instituto de Química UNESP Instituto Nacional de Tecnologias Alternativas Para Detecção Avaliação Toxicológica e Remoção de Micropoluentes e Radioativos (INCT-DATREM) Instituto de Química UNESP FAPESP: #2014/50945-4 FAPESP: #2015/10314-8 FAPESP: #2016/00819-8 FAPESP: #2017/10118-0 FAPESP: #2017/21846-6 FAPESP: #2017/22976-0 FAPESP: #2017/26288-1 CAPES: 001 CNPq: 302874/2017-8 CNPq: 406612/2013-7 CNPq: 427452/2018-0 CNPq: 465571/2014-0

This is a detailed study of how impurities can affect the mechanisms of lithium storage in composite electrodes consisting of a three-dimensional single-walled carbon nanotube (SWCNT) bundles network. To remove impurities such as fullerenes, amorphous carbon, catalyst, and nanographite, we submitted the SWCNT bundles to an appropriate chemical treatment before using them to prepare the electrode. Then, we analyzed how this treatment influenced electrode potential, fading capacity, and specific capacity. Additionally, we evaluated the electrode prepared with high-purity SWNCT bundles by galvanostatic intermittent titration, to obtain lithium transport parameters under thermodynamic conditions. We achieved an intrinsic specific capacity of 400 mAh g −1 for the purified SWCNT bundles prepared by an arc-reactor method. The transport parameters revealed that the electrode underwent electronic transition of the semiconducting-metal type. The chemical diffusion coefficient ranged from 10 −4 to 10 −18 cm 2 s −1 with decreasing electrode potential.